The present invention relates to a spar-type floating offshore wind power generation facility that is installed on a relatively deep-water sea.
Power generation methods such as hydroelectric power generation, thermal electric power generation, and nuclear electric power generation have hitherto been almost exclusively adopted. In recent years, however, wind power generation that generates electric power through the utilization of natural wind has drawn attention from the viewpoints of environment and effective utilization of natural energy. Wind power generation facilities are classified into land installation types and water installation (mainly sea installation) types. It should be noted that, in Japan that contains mountainous regions from coastal areas towards backhand, the tracts of flat lands where stable wind is expected are small in coastal areas. On the other hand, Japan is surrounded by sea on all four sides and thus is advantageous in that wind suitable for power generation can easily be obtained on the sea and, at the same time, there is little or no restriction on installation. Accordingly, many floating offshore wind power generation facilities have recently been proposed.
For example, JP2001-165032A proposes a wind power generation apparatus including: a trigonal planar floating body that includes a combination of hollow quadrilateral prismatic structures and floats on water; and a windmill for power generation, provided on the floating body. The floating body is called a “pontoon type” because the floating body floats on the water.
JP2007-160965A proposes a floating body structure including: a plurality of floating bodies with, articles being mounted on the upper part thereof; connections that are formed of a longitudinal rigid body that has a predetermined center with an inner end of the rigid body connected thereto, is extended from the inner end in a horizontal radial direction and has an outer end with the floating body connected thereto; and a tensioning portion that produces a tensile force between the floating bodies.
JP2007-331414A proposes a floating body structure including: a plurality of floating bodies that float on water; connections that are formed of a rigid body and annularly connect the floating bodies to each other; a mooring unit that moors an annular substantially central portion at a water bottom; a position detecting means that detects the position of the floating body; a tidal current detecting means that detects a tidal current; helms that are mounted on the plurality of floating bodies in such a manner that the angle to the tidal current is variable; and a position control unit that allows the position of the floating bodies to be varied by regulating the angle of the helms to the tidal current with the annular substantially central portion presumed to be central. The floating body structures in JP2007-160965A and JP2007-331414A described above are called a “semi-submerged type” because the floating body structure floats with the floating bodies being submerged below water.
Further, JP2009-18671A proposes a floating body structure for offshore wind power generation, the floating body structure including: a lower floating body including upper and lower lids and cylindrical precast concrete blocks continuously installed between the upper and lower lids, the upper and lower lids being integrally joined to the concrete blocks with a PC steel material; and an upper floating body integrally joined to the lower floating body with a PC steel material, the upper floating body including precast concrete blocks having a smaller diameter than, the precast concrete blocks in the lower floating body, and upper lids, wherein a plurality of ballast tanks are formed on the lower inner side of the lower floating body by partition walls and a plurality of water-tight compartments are formed on the inner side of the upper floating body by partition walls. The floating body structure of JP2009-18671A floats in a standing state like bobbers for fishing and is thus called, a “spar type.”
Only one spar-type floating body of the above type can be mounted on one floating body. The spar-type floating body, however, is superior in cost effectiveness to other types of floating bodies, that is, a pontoon-type and semi-submerged floating bodies and, at the same time, is excellent in stability of the floating body.
Accordingly, the present applicant also has proposed, in JP2010-223113A, a spar-type offshore wind power generation facility 50 as shown in FIG. 25, the spar-type offshore wind power generation facility 50 including: a floating body 51; a deck 52 that is installed on the upper part of the floating body 51; a mooring cable 53 connected to the deck 52; a tower 54 provided upright on the deck 52; and nacelles 55 and a plurality of windmill blades 56,56 . . . provided at the top of the tower 54, wherein the floating body 51 includes a lower concrete floating body structure 51A and an upper steel floating body structure 51B, the lower concrete floating body structure 51A including a plurality of concrete precast cylindrical bodies that have been stacked on top of each other in the direction of height and joined integrally to each other with a PC steel material, the upper steel floating body structure 51B being consecutively provided, on the upper side of the lower concrete floating body structure 51A, the floating body 51 having a spar-type floating body structure having a closed-end hollow portion with the upper end being open, and the tower being allowed to be lifted/lowered at least in construction, by a tower lifting/lowering equipment provided on the deck 52 and can be housed in the floating body 51.